The present invention relates to an electrophotographic copying machine for controlling a toner density by a standard index board image, which can form a binding margin at an upper end of an image.
When copied documents are filed or bound, it is convenient to form a binding margin at identical end portions of copied sheets. Therefore, recently, a copying machine wherein a binding margin copy mode for shifting a position of an image to be transferred to the copy sheet can be set to form a binding margin and a copying operation can be performed has been commercially available.
On the other hand, in general, a recent electrophotographic copying machine includes a standard index board at a front end portion of an original table and latent images of an original and the standard index board are respectively formed on a photosensitive body and the upper end of the original image by scanning. Then, the density of a standard index board toner image obtained by exposure is measured to control a toner density for the next copying operation.
A conventional exposure operation in a normal copy mode will be described hereinafter with reference to an arrangement of an electrophotographic copying machine shown in FIG. 1.
In FIG. 1, a scale plate 2 for designating an original position depending on the size of an original D, and an original cover 3 for covering the placed original D are located on a main body of the copying machine. A standard index board 40 having a predetermined density is arranged on the rear surface of the scale plate 2. The standard index board 40 is spaced apart from an original-side end of the scale plate 2 by an interval d (about 10 mm). A first mirror unit 6 having an exposure lamp 4 and a first mirror 5 is disposed below an original table 1 in the main body of the copying machine. The first mirror unit 6 is disposed parallel to the original table 1 and can be linearly reciprocated in FIG. 1 to optically scan the standard index board 40 arranged at the upper end of the original and the entire surface of the original D. Reference numerals 7 and 8 denote second and third mirrors. A second mirror unit 9 integrally formed with the mirrors 7 and 8 is linearly reciprocated at a half speed of the first mirror unit 6. The second mirror unit 9 is moved parallel to the original table 1 in the same manner as in the first mirror unit 6, as a matter of course. Light reflected by the standard index board 40 and the original D which are positioned on the original table 1 is reflected by the first, second, and third mirrors 5, 7, and 8, and incident on a photosensitive drum 20 serving as an image supporting member through a main lens 10, a fourth mirror 11, and a slit S.
In the copying machine having the above-mentioned exposing steps, in order to perform a copying operation with a binding margin at an upper end of the copied image (a binding margin copy mode), a feed timing of the copy sheet (transfer sheet) is advanced to advance the transfer sheet from an image on the photosensitive drum 20 by the binding margin. However, if the transfer sheet is excessively advanced, the image of the standard index board 40 is also undesirably transferred to the transfer sheet. Therefore, in the relationship between the images on the peripheral surface of the photosensitive drum 20 in FIG. 2(a), the interval d between a standard index board latent image 40a and an original latent image 41a, i.e., the interval d between the standard index board 40 and the distal end of the original D, must be increased to exceed at least a maximum binding margin set by a user. Therefore, when the copying machine which can set a sufficient binding margin is obtained, it is necessary to increase the interval d. For this reason, the scanning lengths of the first and second mirror units 6 and 9 are increased, and the size and cost of the copying machine are undesirably increased.